1. Field of the Invention
The present invention relates to a beam deflector scanning light emitted from a light source to a target surface, a light scanning unit using the same, and an image forming apparatus using the light scanning unit. More particularly, the present invention relates to a beam deflector having a structure capable of reducing noise caused by rotation of a motor, a light scanning unit using the same, and an image forming apparatus using the light scanning unit.
2. Description of the Related Art
Generally, a light scanning unit is used for devices such as a laser printer, a digital copy machine, a barcode reader, and a facsimile machine to form a latent image on a photoreceptor through main scanning of a beam deflector and sub-scanning by the rotation of the photoreceptor.
Referring to FIG. 1, a conventional light scanning unit includes a light source 1 for generating a light beam, a beam deflector 7 to deflect incident light so that the light beam emitted from the light source 1 is scanned onto a photoreceptor 15, and an f-θ lens 11 for compensating for an error in the deflected light beam from the beam deflector 7. Additionally, the conventional light scanning unit may further include a collimating lens 3 on an optical path between the light source 1 and the beam deflector 7, to collect the light beam diverging from the light source 1, and a cylindrical lens 5 for shaping the light beam. A reflecting mirror 13 may be disposed between the f-θ lens 11 and the photoreceptor 15 to change the direction of the light beam.
The beam deflector 7 includes a driving source 9 and a polygonal mirror 8 rotated by the driving source 9. Accordingly, the direction of the beam emitted from the light source 1 is changed according to the rotation of the polygonal mirror 8, and a scanning direction is determined.
With technological developments, the print speed of a device using such light scanning units has increased. Accordingly, a polygonal mirror is required to rotate at higher speeds and operate for a long period of time.
However, when the polygonal mirror is rotated at high speed, noise occurs. The noise may occur because of factors such as friction with the air and pressure differences resulting from the high-speed rotation of the polygonal mirror.
A technique relating to the reduction of noise is disclosed in Japanese Patent Publication No. P2001-142023A, entitled “Laser Scanning Unit,” published on May 25, 2001.
Referring to FIG. 2, a laser scanning unit disclosed in the Japanese patent publication includes a polygonal mirror 25 rotated by a motor 21, a cover member 31 protecting the polygonal mirror 25, and radiating pins 35 installed below and partially exposed outside the motor 21.
The cover member 31 covers the polygonal mirror 25 to protect the polygonal mirror 25 from external contaminants. Moreover, the cover member 31 prevents noise, due to the driving of the motor 21, from transmitting to the outside of the laser scanning unit. In addition, the cover member 31 is made using an aluminum material having high heat conductivity to prevent heat from being generated. An aperture 31a, through which a laser beam passes, is provided on a sidewall of the cover member 31. The radiating pins 35 discharge heat, generated during the driving of the motor 21, to the outside of the laser scanning unit.
An image forming apparatus, such as a laser printer or a copy machine, uses a laser scanning unit for improving performance and minimizing size. However, when the laser scanning unit includes the radiating pins 35, the ability to minimize the image forming apparatus is limited.
Meanwhile, noise occurring in the motor 21 can be prevented from being transmitted outside through noise insulation and acoustic absorption. However, when the cover member 31 of the conventional laser scanning unit is made using an aluminum material, noise insulation may be achieved, but, efficiency is lower compared to when a material having a higher density than an aluminum material is used. Moreover, since the cover member 31 made using an aluminum material does not have acoustic absorption properties, it is very likely that noise occurring in the motor 21 will vibrate in the internal space of the cover member 31, thus, resulting in resonance.
Accordingly, there is a need for an improved beam deflector configured to reduce noise caused by rotation of a motor.